USB problems. Help! Paypal $5 to who ever resolves problem!

Okay, So I got a Dell. A mistake I've realized now.
Anyway, my system fan fried a while back and I had the motherboard/ram/video card/system fan/powersupply replaced.
Ever since Dell replaced the parts, the USB ports have not worked. I have tired everything. Bios, drivers, chipset drivers and all that jazz. Dell wants me to reformat. I told them that I will not do it and lets go to the next step. There should be no reason why my USB ports would not work on a fresh install of XP Pro the same day I got the new motherboard. It's not my hardware I'm connecting either. I have a USB mouse and it works on the PS2 connection. I've tried all the ports too, nothing works.
Anyone have any idea of what it could be? I am certain its a hardware fault. There is no reason why my second harddrive or new OS(XP from the ME I bought the comp with) would cause any problems. I have until January to resolve this problem. I feel like going out, buying a new case, mobo, and processor(I have the old style P4) and video card(32mb currently).
Does anyone have any ideas of what it could be?

Are you talking about the front panel USB ports? Those have to be wired by hand (pain in the ass) and if they replaced your mobo they might have forgot to rewire the front USB. If *NONE* of your USB ports work.. then...

maybe when you sent it back to get those parts replaced they unplugged the usb ports from thier power source???? look inside the comp. and see if you notice any free-hanging cables!!!!(sometimes the simplest solution is the best)LOL

Check the BIOS. I'll bet thats it. Several boards seem to be coming now with USB disabled for some reason in the BIOS. Also, it was agood idea by someone else to check if the back USB ports work because it is very possible that the front ones are not connected properly by the cable inside of the case.

See if you get power on your devices -- for example, an Optical mouse will light up once your plug it into a live USB port whether or not an OS is on the system.